Carpet having durable antistatic properties

ABSTRACT

A CARPET HAVING DURABLE ANTISTATIC PROPERTIES, SAID CARPET CONTAINING ABOUT 0.01% TO ABOUT 10% BY WEIGHT OF AN ELECTRICALLY CONDUCTIVE FIBER IN ITS SURFACE STRUCTURE, CHARACTERIZED IN THAT SAID ELECTRICALLY CONDUCTIVE FIBER COMPRISES A SUBSTRATE OF CHEMICAL FIBER AND AN ELECTRICALLY CONDUCTIVE COATING FORMED THEREON, SAID ELECTRICALLY CONDUCTIVE FIBER HAVING THE FUNCTIONAL PROPERTIES TEXTILE FIBERS.

United States Patent @lfice 3,582,445 Patented June 1, 1971 US. Cl. 161-66 9 Claims ABSTRACT OF THE DISCLOSURE A carpet having durable antistatic properties, said carpet containing about 0.01% to about 10% by weight of an electrically conductive fiber in its surface structure, characterized in that said electrically conductive fiber comprises a substrate of chemical fiber and an electrically conductive coating formed thereon, said electrically conductive fiber having the functional properties of textile fibers.

This invention relates to a carpet having durable antistatic properties.

A carpet when being used, and especially when being used at low humidity, has the undesirable tendency of building up a static charge in itself as well as the human body which walks thereover to cause such electrostatic troubles as shocks to the body and promotion of soiling of the carpet. As a mean of solving this problem there is a proposal to incorporate in the surface structure of a wool carpet at small quantity of the 304 type stainless steel fiber in its staple form (Modern Textile Magazine, June 1967, pages 53-56). Again, a nylon carpet which contains a small quantity of copper wire (about 100 micron in diameter) is also available commercially. However, since the textile fibers which are usually used in carpets are essentially dissimilar in character from the metallic fibers, there arise problems in connection with their mixing and processing as well as in the hand of the products obtained. Further, the manufacture of metallic fibers of fine denier, and especially in the form of monofilament, is not an easy matter, and their manufacture frequently is a costly operation.

A carpet having durable antistatic properties is provided according to the present invention by a carpet which is characterized in being one whose surface structure is incorporated with about 0.01 to 10% by weight of an electrically conductive fiber, which fiber comprises a substrate of chemical fiber whereon is formed an electrically conductive coating to thus result in an electrically conductive fiber possessing the functional properties of textile fibers.

The term fiber, as used herein and the appended claims, unless otherwise noted, includes that of staple fiber form as Well as that of continuous filament form.

The electrically conductive fiber used in the carpet according to the present invention comprises a substrate of chemical fiber consisting of a polymer such as nylon, polyester, acrylic, polypropylene, cellulose acetate or regenerated cellulose, whereon is formed an electrically conductive coating, and the so formed fiber possesses the functional properties of textile fibers. The terminology, functional properties of textile fibers, as here used, is meant, in general, to be the possession of mechanical properties whereby a fiber can be submitted to the usual spinning, twisting, crimp-imparting, weaving and knitting operations and stand such conditions which it will usually encounter during these processing steps as well as in its use, i.e. such conditions as abrasion, tensile stress, bending stress, repetitive fiexure, repetitive elongation and relaxation and repetitive compression and relaxation; and the possession of compatibility and coprocessability with the usual organic textile fibers. The electrically conductive fiber to be used in the carpet according to the present invention should possess mechanical properties which are about comparable to those of the substrate chemical fiber. It should generally possess a tensile strength of at least about 1 g./den., preferably at least about 2 g./den., an elongation at break of at least about 3%, preferably about 10%, and an initial modulus not exceeding about 3000 kg./ mm?, preferably not exceeding about 2000 kg./mm. The electrically conductive fiber used should preferably excel in not only the foregoing mechanical properties in the longitudinal direction but also in its mechanical properties in the lateral direction such as flexibility and also in its chemical properties such as its property to withstand the usual scouring, dyeing and washing operations. In addition, the electrically conductive fiber to be used in the present invention should generally possess a low density of less than 2.5 g./cc., and preferably a low density of less than 2.0 g./ cc.

The electrically conductive coating can be formed on the substrate fiber in the following manner. For example, a polymeric binder solution or emulsion which contains dispersed therein finely divided silver, gold, platinum, brass, nickel, aluminum, tungsten or other finely divided metals as well as other finely divided electrically conductive materials such as copper oxide or carbon black is applied to the surface of the substrate fiber, following which the coating is dried, and, if circumstances require, the polymeric binder is cured. Alternatively, the conductive coating of metals such as nickel, copper, cobalt, chromium, zinc, tin or others can be formed on the substrate fiber by chemical plating, whereas the coating of metals such as aluminum, copper or others on the substrate fiber can also be formed by vacuum evaporation. Further, if necessary, a top coating of an organic polymer may also be applied on to the surface of the electrically conductive coating. The electrically conductive fiber to be used in the present invention preferably is one having an electrical resistance not exceeding about 2000 megohms per centimeter.

The carpet according to the present invention, as hereinbefore noted, contains a small quantity of the hereinbefore described fiber in its surface structure. The term surface structure, as used herein denotes the structure of the surface layer of the carpet, and more specifically denotes the tufted fiber bundle (tufted yarn) of the surface layer in the case of the tufted carpet comprising a. ground cloth upon which fiber bundles are tufted; the pile yarn of the carpets surface layer in the case of the woven carpets having a pile structure of loop or cut pile such as hand knotted, Wilton and Brussels carpets; the weave structure of the carpets surface layer in the case of the Woven carpets such as those of plain, combination and inlaid weaves; and the surface layer web, particularly the surface layer portion, the zone Within about 1 mm. of the surface, in the case of the non-woven carpets consisting of bonded webs. The zones other than the surface structure of the carpet, for example, the ground fabric of a tufted carpet, and those portions other than the pile yarn of the piled woven carpet need not necessarily contain the electrically conductive fiber. For achieving notable antistatic eifects, the electrically conductive fiber must be present in the surface structure of a carpet in an amount of at least 0.01% by weight. While it is possible at times to achieve the antistatic effect even with smaller amounts than indicated above, the effects are frequently not stable. On the other hand, when the electrically conductive fiber is incorporated at the rate of about 2% to about 10% by weight, the proportionate improvement in the antistatic elfects corresponding to the increase of the electrically conductive fiber gradually decreases as the latter value is approached. Hence, the use of the electrically conductive fiber in an amount in excess of about by Weight is actually not only unnecessary but is costly as well. Therefore, from a practical standpoint the electrically conductive fiber should be used in the surface structure of the carpet at the rate of about 0.01% to about 10% by Weight, and preferably about 0.05% to about 2% by weight.

In the case of the tufted and woven carpets, the electrically conductive fiber is advantageously incorporated in the material making up the carpet in the form of continuous filament. When the material making up the surface structure of a carpet is, say, tufting or pile yarn spun from staple fibers, it is also possible to effect the incorporation of the electrically conductive fiber by blending these staple fibers with the electrically conductive fiber in the form of staple fiber. However, even in the .case the tufting or pile yarn is a spun fiber, it still is advantageous to use the electrically conductive fiber in its continuous filament form, combining it in this form with the separately prepared spun yarn. It has been confirmed that better and stabler antistatic effects could be obtained by incorporating the electrically conductive fiber in its continuous filament form than when an equal weight of the electrically conductive fiber was incorporated in the form of staple fiber. Especially, when the material making up the surface structure of the carpet is continuous filament yarn, the electrically conductive fiber in the continuous filament form is advantageously used. While the electrically conductive filament can be incorporated in the carpet when tufting or weaving the carpet by carrying out the tufting and weaving with the electrically conductive filament lined up along with the filament yarn 'which is to make up the surface structure of the carpet, it is of greater advantage to use a filament yarn in which the electrically conductive filament has been incorporated in advance. For example, this can be ac complished by combining at least one end, and advantageously more than one end, of an electrically conductive crimped or uncrimped fiber in monofilament form with a bundle of filaments such as crimped nylon or polyester and then twisting this yarn bundle. Alternatively,

the incorporation of the electrically conductive fiber can be carried out by combining one or more uncrimped electrically conductive monofilaments with a bundle of tufting filaments and thereafter mechanically imparting crimp to the bundle followed by twisting.

That the electrically conductive filament as used in the present invention could stand the crimp-imparting, twisting, tufting and weaving operations was unexpected. Further, that the incorporation of only one end of an electrically conductive monofilament in a yarn bundle of tufting yarn, which usually is of the order of 1000 to 5000 denier, was fully effective, was surprising. In addition, it was surprising that all of the tufted bundles of fibers need not contain the electrically conductive filament. The desired antistatic effect can be achieved by the placement of the tufted bundle of fibers containing the electrically conductive filament at intervals of less than about 30 centimeters, and preferably less than about 10 centimeters. This is equal to the incorporation of at least one end of the electrically conductive fiber in the form of a continuous filament in every first to eightieth, and preferably every first to twenty-seventh, tufted bundle of fibers. This likewise applies in the case of the woven carpets. The electrically conductive filament can be present in the woven structure of carpet surface at intervals less than about 30 centimeters, and preferably less than about 10 centimeters. For example, in the case of the pile weave carpet, it suffices that at least one end of the electrically conductive fiber in continuous filament form is contained in every first to eightieth, and preferably in every first to twenty-seventh end, of the pile yarn.

In the case of the non-woven carpet, the electrically conductive fiber is incorporated in the web which constitutes the surface layer of the carpet. This is usually conveniently performed by making the web which is to constitute the surface layer portion of the carpet, from a staple fiber blend obtained by cutting an electrically conductive filament-containing tow into staple fibers. However, it is also possible to make the web from a staple fiber blend consisting of a mixture of the staple used for the web and the electrically conductive fiber in staple form. Alternatively, either the electrically conductive fiber in staple or filament form or a netlike material made from the electrically conductive fiber can be placed in the neighborhood of the surface of the web made in advance. The so obtained electrically conductive fiber-containing web can then be made into a non-woven carpet by a suitable web bonding technique such as the usual adhesive procedures, the needle punch method, the stitch method, or a combination of these procedures. When the nonwoven carpet is to be made by stacking a number of sheets of the webs, or on occasions by stacking the webs with a suitable ground cloth, and then effecting the adhesion of the stack, it sufiices that only the Webs constituting the surface layer of the carpet, particularly the layers within about 1 mm. of the surface, contain the electrically conductive fiber, it being unnecessary to incorporate the electrically conductive fiber in the ground cloth or the web making up the portion of the carpet remote from the surface.

The desirable electrically conductive fiber used in the carpet according to the present invention comprises a substrate of chemical fiber whereon has been formed an electrically conductive coating consisting of a polymeric binder matrix having dispersed therein finely divided particles of an electrically conductive material sufficient to render the electrical resistance of the fiber less than about 2000 megohms per centimeter, the thickness of which coating averages about 0.3 to about 15 microns. Moreover, said electrically conductive fiber possesses the functional properties of textile fibers. An electrically conductive fiber of this kind can be conveniently produced by applying to the substrate fiber either a solution or emulsion of a polymeric binder wherein is dispersed finely divided metals or other electrically conductive finely divided materials, followed by drying and, as may be required, curing of the polymeric binder. As the substrate fiber, particularly to be preferred from the standpoint of their adhesiveness of the conductive coating and mechanical strength are the fibers of synthetic linear polyamides such as nylon 6 and 66, those of about 5 to 50 denier, and preferably about 10 to 30 denier, being advantageously used. Again, the substrate fiber is preferably of monofilament form. Finely divided particles of silver and electrically conductive carbon black are preferred as the finely divided electrically conductive material to be used in the invention in view of their resistance to scouring and dyeing treatments, resistance to washing, weatherability, chemical resistance and electrical conductivity. These finely divided electrically conductive materials are mixed and dispersed in an adhesive composition, i.e. a liquid composition containing a suitable polymeric binder, and this dispersion is applied to the substrate fiber. Usable as the polymeric binder are the various synthetic resins of the acrylic, epoxy, phenolic, urethane, melamine, urea, polyester, vinyl and silicone types, the natural and synthetic rubbers, and mixtures of these However, in each individual case, a choice should be suitably made, taking into consideration the characteristics of binders such as their adhesiveness to the substrate fiber; the abrasion resistance and chemical resistance of the cured coating, and flexibility of the coated substrate fiber. Further, this liquid composition can be incorporated with thickening agents, anti-aging agents, a modifier for imparting flexibility to the coating, and a curing agent for the polymeric binder as well as other additives. Examples of suitable polymeric binders are the combinations of the oil-soluble phenolic resins with chloroprene polymer, styrene/butadiene copolymer, acrylonitrile/butadiene copolymer and other synthetic rubbers; the combinations of a bisphenol/epichlorohydrin type epoxy resin having an epoxy equivalent of about 170 to 250 with a polyamide resin, an epoxidized vegetable oil or liquid polyalkylene sulfide; a relatively low molecular weight polyurethane urea having terminal N,N- disubstituted ureylene groups; the combination of a partially saponified vinyl chloride/vinyl acetate copolymer and a melamine resin modified by n-butanol; and the combination of ethyl acrylate/styrene/hydroxyethyl acrylate and a melamine resin modified by n-butanol.

The lower limit of the amount of the finely divided particles of an electrically conductive material to be present in the electrically conductive coating is imposed as a limitation in view of the conductivity of the fiber. When the finely divided electrically conductive material is a metal such as silver, the content of the metal in the coating must be made at least 50% by weight, whereas when it is carbon, the carbon content in the coating must be made at least by weight. Further, it is preferred from the standpoint of the stability of the conductivity that the thickness of the coating be at least about 0.3 micron in the case of finely divided metals and that it be at least about 0.7 micron in the case of carbon. On the other hand, the upper limit of the thickness of the electrically conductive coating and the upper limit of the amount contained in the coating of the finely divided particles of the electrically conductive material are imposed as practical limitations in 'view of the mechanical properties, especially flexibility of the fiber, the tenacity of the coating and the adhesiveness between the coating and the substrate. A coating of excessive thickness is not only unnecessary from the standpoint of conductivity but also undesirable from the standpoint of flexibility. A coating containing finely divided metals as its electrically conductive material preferably should have an average thickness not exceeding about microns. Again, coatings containing the finely divided metals in an amount exceeding about 90% by weight or the carbon in an amount exceeding about 60% by weight are in general poor in their tenacity and their adhesiveness to the substrate and hence easily tend to become separated from the substrate during the processing steps and in use.

Another desirable type of electrically conductive fiber that is used in the carpet according to the present invention is that comprising a substrate of chemical fiber and a metallic coating of an average thickness not exceeding about 1.5 microns which has been chemically deposited on the former, the so made up fiber having an electrical resistance of less than about 2000 megohms per centimeter and the functional properties of textile fibers. The method of manufacturing an electrically conductive fiber of this kind comprises chemical plating the substrate fiber with a metal. As the substrate fibers, in this case, particularly to be preferred from the standpoint of the ease of application of the metallic coating and their ability to adhere metals are those acrylic polymers in which the content of aerylonitrile is at least 80 mol percent and those of polyesters whose content of ethylene terephthalate is at least 80 mol percent. The substrate fiber can have a textile denier of about l-50 denier.

The metallic coating can be applied to the substrate by the method which per se is known for chemical plating of organic polymeric materials, optionally followedby electroplating. Chemical plating can be carried out on substrate fibers of multifilament, monofilament or staple form. In carrying out the chemical plating of shaped articles such as cast articles of organic polymeric materials, the general practice is to perform such pretreatments as mechanical roughening, degreasing, etching, sensitizing and activation of the surface. The step of mechanically roughening the surface is performed with a view to forming a rough surface suitable for performing the metallic plating, but in the case of a substrate of fiber form,

this step is not particularly necessary, since the surface of the fiber is roughened to a suitable extent to be conventionally ready for carrying out the metallic plating operation. Further when the acrylic fiber is to be used as the substrate, a satisfactory metallic coating can be formed on the substrate even though the etching step is omitted. The etching of the polyester fibers is best carried out with an alkali to an extent that a weight decrease of 0.3 to 10% by weight takes place. As the etchant the aqueous or alcohol solutions of such alkalis as sodium hydroxide, potassium hydroxide and sodium carbonate can be used, but the use of the aqueous sodium hydroxide solution is especially to be desired. The polyester fibers are dipped in such an alkaline bath, and the concentration and temperature of the bath and the time of immersion are suitably chosen such that the decrease in weight due to dissolution comes within the range of 03-10%. For example, in the case where an aqueous sodium hydroxide solution is used, the end can be fully achieved by treating the degreased polyester fiber for 3 seconds-30 minutes at 50-l00 C. using a bath whose concentration is 05-30% by weight. The substrate fiber, which has thus received the chemical treatment, is then water-washed or water-washed after having been neutralized with a dilute acid solution, and thereafter delivered to the next step. The degreasing, sensitizing and activation steps can be carried out in accordance with the well-known procedures for applying chemical plating to the shaped articles of organic polymers.

The chemical plating is carried out on the pretreated substrate. As example of metals suitable for chemical deposition on the substrate, thereare nickel, copper, cobalt, chromium, zinc and tin, of which nickel is of advantage from the standpoint of ease of plating and economy. As the composition of the chemical nickel plating bath, several types can be mentioned, such as soluble nickel salt-hypophosphite, soluble nickel salt-boron nitrogen compound, and soluble nickel salt-urea. While basically any of these compositions can be used with satisfaction, the bath whose composition is of the soluble nickel saltphosphite type is convenient, and particularly preferred is that of this type whch is acidic. An excellent electrically conductive fiber can be obtained with a very short period I of treatment by the use of a relatively high plating bath temperature. For example, when an acidic plating bath consisting predominantly of 20 grams per liter of nickel sulfate, 24 grams per liter of sodium hypophosphite and 27 grams per liter of lactic acid, whose pH has been adjusted to 5.6 is used, satisfactory treatment is obtained with a plating bath temperature of 60-98 C. and a treatment time of 10 seconds-9 minutes. Particularly, if the treatment is carried out at a plating bath temperature of -90 C., a fiber excelling in conductivity can be obtained satisfactorliy even with a treatment time of less than one minute. Since, as hereinbefore described, the chemical nickel plating can be carried out under treatment conditions requiring a very short period of time, it is especially convenient to use it in the continuous chemical plating of filaments. The metallic coating which has been chemically deposited on the substrate fiber can, if desired, be increased in its thickness by further deposition of metal thereon by electroplating. The metal to be electroplated may be one 'which is the same as that which was chemically plated or one differing therefrom.

The thickness of the metallic coating formed on the substrate fiber must be controlled so as to ensure that the product retains the functional properties of textile fibers. A metallic coating of excessive thickness results in a product having poor mechanical properties (elongation and flexibility) and is also unnecessary from the standpoint of conductivity. The upper limit of the average thickness of the metallic coating depends upon the class and denier fineness of the substrate fiber, the class of metal, and the use to which the final product is to be put, but in most cases it should not exceed 1.5 microns.

On the other hand, the lower limit of the average thickness of the metallic coating is that which will suffice to render the fiber conductive. It has been found that there were frequently discontinuities in the metallic coating whose average thickness was less than 0.01 micron and, as a result, that the coated product frequently did not have a conductivity of satisfactory stability. Hence, it is preferable to control the average thickness of the metallic coating to within the range of 0.01 to 1.5 microns, and particularly 0.1 to 0.5 micron.

To the electrically conductive fiber can be applied a top coating of an organic polymeric material. It is to be particularly preferred in the case of the electrically conductive fiber having a metallic coating manufactured by chemical plating or vacuum evaporation coating that a top coating be applied to protect the metallic coating from being oxidized and corroded as well as peeling from the substrate. While the application of a top coating to an electrically conductive fiber having an electrical resistance of less than about 2,000 megohms per centimeter imparts an electrical resistance of the order of several thousand megohms per centimeter to the fiber, it has been surprisingly found that a fiber having a high resistance such as this could be effectively used for achieving the objects of the present invention provided that the starting electrically conductive fiber was one possessing an electrical resist ance of less than about 2,000 megohms per centimeter. As the organic polymeric material to be applied, preferred are the synthetic rubber type polymers which excel in their adhesiveness to metal and the water-repellent silicone resin type polymers, but others can also be used.

The electrically conductive fibers used in the present invention include not only those in which an electric re sistance is in the region of an ordinary conductor, but also those in which an electric resistance is very high such as 2,000 Mil/cm. It is surprising that a marked antistatic effect is exhibited even when a small amount of a fiber having such high electric resistance is incorporated. It is not easy to explain the mechanism of prevention of electrification with simplicity. Generally, a high voltage above 1000 volts poses a problem in an unfavorable electrifica tion of ordinary organic textile fibers, and a quantity of electrostaticity generated at this time is very small. Hence, it is presumed that even in the case of such high electric resistance, the local intrinsic electric breakdown of the coating occurs under such high voltage, and the electrostatic charge is easily dissipated with this electrically conductive fiber by such effects as gaseous corona discharge, surface flashover and tracking and leakage, thus preventing the accumulation of electrostatic charge. This seems to contribute greatly to the prevention of electrostatic charge. Further, the dispersion of electrostatic charge through the electrically conductive fiber as well as the shielding effect of the fiber seem to contribute to the antistatic effect.

The electrically conductive fibers used in the present invention retain the functional properties of the textile fibers and have durability against the various conditions that are usually encountered during the manufacture of carpets and during their use such, for example, as abrasion, repetitive flexure, repetitive elongation and relaxation, scouring, dyeing and washing. The conductive fibers of this invention can be incorporated in the carpets very readily during their manufacture. The carpets according to the present invention which contain a small amount of the electrically conductive fibers have durable antistatic properties and their appearance and hand are also highly satisfactory. Further, these electrically conductive fibers are compatible with the other fibers that make up the surface structure of the carpet, and hence their tendency to separate from the surface during the use of the carpet is slight.

The following examples are given for further illustration of the invention. The resistance of the electrically conductive fiber shown in the examples was determined 8 by using an FM tester, Model L-19-B and an automatic insulation-ohmmeter, Model L-68, manufactured by Yokogawa Electric Works, Japan, and breakage tenacity, breakage elongation and initial Youngs modulus were EXAMPLE 1 Ten parts of finely divided flaky silver (average particle size 1.5 microns), 10 parts of a nitrile rubber-phenol type adhesive (solid content 24%) and 10 parts of methyl isobutyl ketone were thoroughly mixed to prepare a paste, through which was passed a 20 denier crimped nylon 6 monofilament, following which the filament was passed through a slit to adjust its coating thickness. The monofilament was then cured by heating with an infrared lamp to obtain an electrically conductive monofilament (A) having an average electrically conductive coating thickness of 0.4 micron and an average resistance of 500 MQ/cm.

The so obtained electrically conductive filament had the following fiber properties: a breakage tenacity of 4.0 g./den. (5.1 g./den. calculated on the basis of the denier fineness of substrate filament), a breakage elongation of 40% and an initial Youngs modulus of 300 kg./mm. thus demonstrating that it has a tenacity as well as pliability and flexibility which hardly differ from those of the substrate filament. The density of the filament was as low as 1.3 g./cc.

An electrically conductive monofilament-incorporated nylon yarn was prepared by twisting this electrically conductive monofilament with crimped nylon yarn (2600 denier/136 filaments). The foregoing non-electrically conductive nylon yarn and the electrically conductive yarn were used and three types of tufted carpets were made by disposing one end of the latter at every second, fourth and sixth interval of the former (specimen Nos. A-l, A-2 and A-3, respectively). On the other hand, as control a tufted carpet was also made using the foregoing nonelectrically conductive nylon yarn alone. The several specimens were then scoured, dyed and applied to a backing. The so obtained specimens were rubbed with a cloth of polyester fiber at a speed of 6 centimeters per second under conditions of 20 C. and 40% RH. When electrification voltages of these specimens were measured 30 seconds after their electrification voltage had reached saturation, the results obtained were as shown in the following table. It is thus seen that pronounced antistatic effects are demonstrated by the incorporation of only a very small amount of the electrically conductive filament.

Further, a 15 denier nylon 6 monofilament was passed through a paste similar to that described above and thereafter cured by heating as hereinbefore indicated to obtain an electrically conductive filament (B) having an average electrically conductive coating thickness of 2.8 microns and an average resistance of 300/cm.

This electrically conductive filament had a breakage tenacity of 3.1 g./den. (5.6 g./den. on the basis of the denier fineness of the substrate filament), a breakage elongation of 45%, initial Youngs modulus of 260 kg./ mm. and a density of about 1.7 g./ cc.

The so obtained electrically conductive monofilament was used and nylon tufted carpets were made by the same method as hereinbefore described, incorporating the electrically conductive filament at every sixth, twelfth and fortieth interval (specimen Nos. B-l, B-2 and B-3, respectively). These carpets and the previously tested carpets were walked over with leather-soled shoes under conditions of 25 C. and 30% RH. When the saturated electrification voltage of the human body was measured, the results shown in the following table were obtained.

When a nylon tufted carpet not incorporating the electrically conductive filament was walked over, a high electrification voltage such as shown in the following table was built up in the human body and a severe electric shock was received when a grounded conductor such as metal was touched. However, when a small amount of the electrically conductive filament was incorporated, the electrification voltage of the human body was low in all cases and such an electric shock was hardly noted.

Rate ofincorporation of the electrically con- Electriductive filament fication Incorporation of the elecbased on the voltage of Specimen trically conductive filaments total tufted yarn human No. in the several carpets (percent) body (volts) Not incorporating (control)- 5, 000 .A-l Every 2nd interval 0. 50 300 A2 Every 4th interval 0. 25 350 A-B Every 6th interval 0. 17 400 B-l- "do 0. 17 400 B- Every 12th interval 0. 09 500 B3 Every 40th interval 0. 03 --1, 000

Further, the carpet designated specimen No. A-l was .rotatively abraded by means of an uneven-surfaced vinyl chloride resin abradant (load 0.5 kg./cm. 23 rpm), after which the carpet was rubbed with a cloth of polyester fiber in the same manner as previously described. When the electrification voltage so built up was measured, the results shown in the following table were obtained, thus demonstrating that the carpet had a very excellent abrasion resistance.

Electrification Degree of abrasion: voltage (volts) Before abrasion +700 After 100 rotations +800 After 500 rotations +800 After 1000 rotations +800 EXAMPLE 2 (A) Degreased IO-denier polyacrylonitrile type monofilament was chemically plated with nickel by continuous passage through the following baths:

Thus an electrically conductive monofilament (A) having an average electrically conductive coating thickness of 0.4 micron and an average resistance of 1000/cm. was obtained.

(B) This electrically conductive monofilament (A) was immersed in a solution of nitrile rubber-phenol type adhesive (solid content 17%), and then passed through a 10 slit to adjust its coating thickness. The monofilament was then cured by heating to obtain a resin-coated, electrically conductive monofilament (B) having an average resin coating thickness of 0.3 micron and an average resistance of 2,000 Mt'Z/cm.

(C) Also in the similar manner as described in the above item (A) IO-denier polyacrylic monofilament was chemically plated with nickel, to obtain another electrical ly conductive monofilament having an average coating thickness of 0.2 micron and an average resistance of 450S2/cm. This filament was incorporated with 20-denier, crimped nylon 6 monofilament, by applying thereto a solution of nitrile rubber-phenol type adhesive (solid content 17%) using a roller. Thus incorporated filament was cured by heating, with the resin content of 9.5%. The filament (C) had an average resistance of 2,500 Mil/cm.

The so-obtained electrically conductive filaments (A), (B), and (C) had the following fiber properties, demonstrating that they have tenacity as well as apliability which hardly differ from those of the substrate filament.

Breakage tenacity base d on the denier Breakage Initial Electrically Breakage of substrate elouga- Youngs conductive tenacity filament tion modulus D ensity filament (g./d.) (g./d.) (percent) (kg/mm?) (g./cc.)

A 2. 8 3. 6 14 1, 000 1. 5 B 2. 6 3. 5 14 1, 000 1. 4 C 3. 4 3. 9 35 350 1. 2

Nylon tufted carpets were prepared in the similar manner as described in Example 1, by disposing one end of the electrically conductive filament (A), (B) or (C) at every second interval of non-electrically conductive nylon yarn. The several specimens were then scoured, dyed, and then rubbed with a cloth of polyester fiber at a speed of 6 centimeters per second under conditions of 20 C. and 40% RH. When electrification voltage of these specimens were measured 30 seconds after their electrification voltage had reached saturation, the results obtained were as shown in the following table. It is thus seen that all the carpets in which only minor amounts of the electrically conductive filaments in accordance with the invention were incorporated, demonstrated very excellent antistatic efiect. Furthermore, the electrically conductiv filaments (B) and (C) exhibited substantially equal degree of antistatic effect with that of the filament of good electrical conductivity, although they possess very high resistance.

The electrically conductive monofilament (B) prepared in Example 1 was twisted with 2 ply yarn of 16-count worsted yarns, by adding single strand of the former into the twisting procedure of the latter. Thereafter the yarn was incorporated with two strands of conventional, 2 ply yarn of 16-count worsted yarns not blended with the electrically conductive filament. The three strands of yarns were paralleled and made into one, integrated yarn. The three strands-paralleled yarn composed of conventional, non-electrically conductive 2 ply yarn of 16-count worsted yarns and the above-described paralleled yarn in which the electrically conductive filament was incorporated, were used as the pile warp, and a Wilton carpet was prepared by disposing one end of the latter at every ninth interval 1 1 of the former (the rate of incorporation of the electrically conductive filament based on the total pile material yarn being approximately 0.09%

This carpet and a carpet for control not incorporating the electrically conductive filament were walked over with intentional heavy shuffling with leather-soled shoes under conditions of 25 C. and RH. When the saturated electrification voltages of both the human body and the carpets were measured, in case of the control the voltages were 5,000 volts and +8,000 volts, respectively. The walker on Whom the electrification voltage was built up received a severe electric shock when he touched a grounded conductor such as metal. In contrast thereto, in case of the carpet incorporating a very small amount of the electrically conductive filament of the invention, the electrification voltages were only l,000 volts and +2,000 volts, respectively. Consequently, no such electric shock was received by the walker.

EXAMPLE 4 One part of acetylene black and 12 parts of chloroprenephenol type adhesive (polychloroprene/p-t-butylphenol-formaldehyde resin=l00/ 45 solvent toluene, solid content 24%) were thoroughly mixed to prepare a paste.

Plural 15-denier nylon 6 monofilaments were paralleled as slightly spaced from each other, and simultaneously immersed in the paste while retaining the paralleled state. Then the filaments were passed through a slit to adjust the coating thickness, and cured by heating while retaining the minor intervals to prevent their mutual adhesion. Thus they were coated with electrically conductive film. The filaments were bundled into one strand and taken up onto a winder, to provide an electrically conductive multifilament yarn having an average electrically conductive coating thickness of 4.0 microns, and an average resistance of 500 Ktl/cm. per single yarn. This electrically conductive filament had a breakage tenacity of 4.0 g./ den. (5.5 g./ den. on the basis of the denier fineness of the substrate filament), a breakage elongation of 42%, initial Youngs modulus of 210 kg. mm. and density of 1.2 g./ cc.

This electrically conductive multifilament yarn was mixed with polyvinyl chloride tow in advance of preparing therefrom polyvinyl chloride staple fiber for making carpet, and subsequently the tow and the yarn were together subjected to a crimper to be crimped, followed by cutting to the length of 76 mm., to obtain staple fiber incorporated with the electrically conductive fiber of the invention. Thus incorporated electrically conductive fiber showed crimpability similar to polyvinyl chloride fiber, but still retained sufficient electrical conductivity.

The so obtained polyvinyl chloride type staple fiber incorporating the electrically conductive fiber and polypropylene staple fiber were blended at the ratio of 70% of the former with 30% of the latter, and formed into webs, which were joined by needle-punch process to form a non-woven carpet. The rate of incorporation of the electrically conductive fiber in the carpet was varied in each run, by suitably adjusting the number of strands of the multifilament yarn to be incorporated.

These several carpets and a non-woven carpet for control containing no electrically conductive fiber were walked over with intentional heavy shuffling with leather-soled shoes under conditions of 25 C. and 30% RH. When the saturated electrification voltage of the human body was measured, the results shown in the following table were obtained.

Ralte of incorporation As indicated in the above table, in case of the control carpet not incorporating the electrically conductive fiber, a high electrification voltage was built up in the human body and a severe electric shock was received when a grounded conductor such as metal was touched. However, when a small amount of the electrically conductive fiber in accordance with the invention was incorporated, the electrification voltage of the human body was low in all cases, and such an electric shock was hardly noted.

EXAMPLE 5 An electrically conductive staple fiber (length 76 mm., average resistance 3.0 KSZ/ cm.) was prepared by chemical plating the surfaces of 3-denier polyacrylonitrile type fiber to an average nickel metal coating thickness of 0.27 micron. This electrically conductive staple fiber had a breakage tenacity of 2.0 g./ den. (2.7 g./ den. on the basis of the denier fineness of the substrate fiber), a breakage elongation of 30%, initial Youngs modulus of 480 kg./ mm. and a density of 1.5 g./cc. This staple fiber was blended into wool at a rate of 1%, and spun into l2-count yarn by worsted spinning method. Two strands of this yarn were twisted to form 2 ply yarn, and three strands of the 2 ply yarn were paralleled. Three-strands paralleled, conventional 2 ply yarn of l2-count worsted yarns containing no electrically conductive staple fiber, and the above paralleled yarn incorporated with the electrically conductive staple fiber were used as the pile warp, and a Wilton carpet was woven by disposing one end of the latter at every third interval of the former (the rate of incorporation of the electrically conductive staple fiber based on the total pile material yarn being a 0.33%).

This carpet and a control carpet not incorporating the electrically conductive filament were walked over with intentional heavy shuffling with leather-soled shoes under conditions of 25 C. and 10% RH. When the electrification voltage built up in the human body was measured, it was as high as 5,000 volts in case of the control carpet, and the person received a severe electric shock when he touched a grounded conductor such as metal. Whereas, in case of the carpet in which a small amount of the electrically conductive staple fiber in accordance with the invention was incorporated, the electrification voltage built up in the human body was only -900 volts, and such an electric shock was hardly noted.

What is claimed is: I

1. A carpet having durable antistatic properties which comprises a backing and a surface structure aflixed thereto comprising an electrically non-conductive fiber and about 0.0110% by weight, based on the weight of the surface structure, of an electrically conductive fiber comprising a substrate of an organic synthetic fiber of 5-50 deniers having an electrically conductive coating of 0.3l5 microns thereon, which coating comprises a polymeric binder matrix having finely divided electrically conductive carbon black, silver or a mixture thereof dispersed therein in an amount sufficient to render the electrical resistance of the electrically conductive fiber not more than about 2000 megohms/cm.

2. The carpet according to claim 1, wherein the surface structure is tufted, piled, weaved or webbed.

3. The carpet according to claim 1, wherein the electrically conductive coating contains silver in an amount of at least 50% by weight.

4. The carpet according to claim 1, wherein the electrically conductive coating contains carbon black in an amount of at least 5% by weight.

5. A tufted or woven carpet having durable antistatic properties which comprises a backing and a surface structure affixed thereto comprising plural rows of loopstructured piles or tufts of continuous electrically nonconductive fibers and 0.0l-10% by weight, based on the weight of the surface structure, of electrically conductive continuous fibers, each 1-27 tufts in the tufted carpet or 1-27 ends in the woven carpet containing at least one electrically conductive continuous fiber, said electrically conductive continuous fibers comprising a substrate of at least one continuous organic polymeric synthetic fiber of -50 deniers having an electrically conductive coating of 0.3-15 microns thereon, which coating comprises a polymeric binder matrix having finely divided electrically conductive carbon black, silver or a mixture thereof dispersed therein in an amount sufiicient to render the electrical resistance of the electrically conductive fiber not more than about 2000 megohms/ cm.

6. The carpet according to claim 5, wherein the electrically conductive coating contains silver in an amount of at least 50% by weight.

7. The carpet according to claim 5, wherein the electrically conductive coating contains carbon black in an amount of at least 5% by weight.

8. The carpet according to claim 5, wherein the electrically conductive fiber is a monofilament of -30 deniers.

9. The carpet according to claim 5, wherein the continuous electrically non-conductive fibers are formed into bundles of continuous filaments prepared from organic synthetic polymers.

References Cited UNITED STATES PATENTS ROBERT F. BURNETT, Primary Examiner J. J. BELL, Assistant Examiner US. Cl. X.R. 

